1. Field of the Invention
The present invention relates to a multilayered wafer having a thick sacrificial layer, which is obtained by forming a sacrificial layer of oxidized porous silicon or porous silicon and growing an epitaxial polysilicon layer on the sacrificial layer, and a fabrication method thereof.
2. Description of the Related Art
FIG. 1 is a cross-sectional view illustrating the stacked structure of a conventional silicon on insulator (SOI) wafer. As shown in FIG. 1, the conventional SOI wafer has a stacked structure in which an oxide layer 3 is formed on a substrate wafer 1 and a single crystal silicon wafer 6 is formed on the oxide layer 3. Here, the oxide layer 3, which is a sacrificial layer, is formed by thermal oxidization, so it is difficult to form a sacrificial layer having a thickness of 1 .mu.m or more. Thus, when the oxide layer is used to make a structure such as a cantilever or a bridge, a completed structure frequently sticks to a substrate which lies under the structure, since the gap between the structure and the substrate is narrow. Also, in the case of a moving structure, great air damping is produced due to the short distance between the structure and the substrate. Also, since the silicon oxide layer is formed by thermal oxidization, it takes a long time to fabricate the structure. Furthermore, since the structure is fabricated by attaching another silicon wafer onto oxidized substrate silicon, that is, since two wafers are used, the fabrication cost is increased.